Concerns over the limited oil resources in recent years has let to the imposition of certain fuel cost standards in an effort to bring about improvement in controlling automobile fuel costs. In order to meet the strict standards of the future, it will be necessary to improve existing materials and technology. One method is to reduce the weight of the tire itself, which would be effective in bringing about great improvement in automobile fuel costs.
Lowering the specific gravity of the rubber component that forms the tire can be considered. From this standpoint, it would be desirable to effect a great decrease in the quantity of use of carbon black, which has a high specific gravity. Carbon black has approximately twice the specific gravity as that of rubber. However, when the quantity of carbon is decreased, hardness, tensile strength and modulus during low extension are decreased and wear resistance is insufficient.
Another way of lowering the weight of the tire that has been considered is to decrease the size of the tire. However, when the tire is made smaller, the strength of the tire cannot be maintained. When the quantity of carbon black that is used is increased, hardness is increased. However, increase in strength is not sufficient. When an ever larger amount of carbon black is used, strength is decreased, the processing capacity of the rubber composition becomes poor and heat generated from vulcanized rubber is increased. In addition, there are the problems that the specific gravity of the rubber composition increases and the weight of the tire increases.
Consequently, it is desirous to have a reinforcing material which has a greater reinforcing capacity than conventional carbon black and that has greater hardness and wear resistance when used in small quantities. Most recently, fine, filiform carbon fibrils have been developed and it has been discovered that rubber compositions having hardness and good tensile strength and wear resistance can be obtained by addition of small amounts of reinforcing material. However, problems such as deterioration in the physical properties, and, of tensile strength in particular, of these rubber compositions at high temperatures remain.